1. Field of the Invention
The present invention relates to a broadband wireless communication system. More particularly, the present invention relates to an apparatus and method for transmitting and receiving information through a fast feedback channel in a broadband wireless communication system.
2. Description of the Related Art
In the next generation communication system, also known as the 4th Generation (4G) communication system, research is being actively conducted to provide a Quality of Service (QoS) with a data transfer speed of about 100 Mbps. An example of such a communication system is an Institute of Electrical and Electronics Engineers (IEEE) 802.16 system. The IEEE 802.16 system employs an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme so that a broadband network can be supported in a physical channel.
In a broadband wireless communication system such as the IEEE 802.16 system, Mobile Stations (MSs) located within a cell periodically transmit feedback information to a Base Station (BS). The feedback information can represent a forward channel state through additional physical channels allocated along frequency and time axes. Examples of the feedback information include Channel Quality Indication (CQI) information such as a Carrier to Interference and Noise Ratio (CINR) and a Modulation and Coding Scheme (MCS), sub-band information having an excellent channel property, and a Precoding Matrix Index (PMI) of Multiple Input Multiple Output (MIMO). The feedback information may only be a small amount of information but is significantly important in the operation of the communication system and thus requires high reliability to support the entire cell area including a cell edge. Alternatively, the feedback information may be information having a large amount of information to support a MIMO mode operated in a high Signal to Noise Ratio (SNR) environment.
A fast feedback channel supporting the entire cell area has to be designed to have a robust structure so that a region of a low SNR can also be supported with a small amount of information. Therefore, in a communication system such as the IEEE 802.16 system, a noncoherent modulation/demodulation scheme is used for the fast feedback channel. That is, a transmitting end assigns a code sequence, corresponding to information to be transmitted, to an allocated resource and then transmits the resultant code sequence, and a receiving end searches for a code sequence corresponding to a maximum value among correlation values between each of all code sequences and a received signal.
With the recent development of multimedia technologies and the increase in demands thereof, a high data rate is necessary and thus a recently developed communication system actively adopts an improved technique such as MIMO for the support of the high data rate. Unlike in a conventional communication system which uses a level of CQI information as feedback information, a technique such as Closed-Loop (CL)-MIMO requires a relatively large amount of feedback information, e.g., a PMI, a rank, etc. However, an amount of feedback information transmittable through the fast feedback channel is limited by a length of the code sequence. If to-be-transmitted feedback information has a length greater than or equal to the code sequence, a plurality of fast feedback channels has to be allocated to a single MS.
As described above, since a large amount of feedback information is required, a currently available method for operating the fast feedback channel is not suitable to effectively transmit a required amount of information. Therefore, there is a need for a method for effectively operating a fast feedback channel with a limited amount of resources in a broadband wireless communication system in which a variety of feedback information exists.